This invention relates to a cable reel including a sound-absorbing material and a method for producing the sound-absorbing material for the cable reel, and more particularly it relates to a cable reel preferably adapted to be mounted on a steering device for an automotive vehicle so as to electrically interconnect a stationary member assembly and a movable member assembly through a flat cable and a method for producing a sound-absorbing material for use of the cable reel.
In an automotive vehicle equipped with an air bag, a cable reel is provided in a steering wheel in order to supply electrical power to an air bag system. For convenience of explanation, such a cable reel will be described below by referring to the drawings. FIG. 8 is a schematic longitudinal sectional view of a conventional cable reel.
FIGS. 9A to 9C show an example of a conventional sound-absorbing material. FIG. 9A is a plan view of a cable reel shown in FIG. 8, illustrating a conventional sound-absorbing material mounted on a bearing surface of the cable reel. FIG. 9B is a perspective view of the conventional sound-absorbing material. FIG. 9C is a fragmentary cross sectional view of the sound-absorbing material taken along line 9C--9C in FIG. 9A.
As shown in FIG. 8, the conventional cable reel includes a movable member assembly 1 which rotates together with a steering wheel, and a stationary member assembly 2 which is secured to a stationary shaft on a body frame. The movable and stationary member assemblies 1 and 2 define an annular cable containing chamber 3 which accommodates a flat cable 4 in a coiled manner. Opposite ends of the flat cable 4 in the coiled manner are connected to lead wires which are led out from the movable and stationary member assemblies 1 and 2, respectively, to be connected to an external connector or electrical wires. In such a cable reel, the flat cable 4 is wound in the cable containing chamber 3 when the steering wheel is turned in one or direction while the flat cable 4 is unwound in the chamber 3 when the steering wheel is turned in the other direction, so that a device (air bag) on the steering wheel is electrically connected to a power source on the body frame.
The cable reel involves a problem in that an unpleasant sliding noise is generated when the lateral opposite edges of the flat cable 4 slide on upper and lower bearing surfaces of the cable containing chamber 3 upon winding and unwinding of the flat cable 4 in the chamber 3. The flat cable 4 vibrates in an axial direction (from an upper to lower direction or from a lower to upper direction) of the steering wheel during idling or driving of the automotive vehicle, thereby giving rise to an unpleasant vibration noise due to collision between the bearing surfaces of the chamber 3 and the lateral opposite edges of the flat cable 4.
Japanese Utility Model Publication No. HEI 6-36040 (1994) discloses a cable reel in which a highly lubricative sheet such as a polytetrafluoroethylene (PTFE) resin or the like is adhered to at least one of bearing surfaces of a cable containing chamber in order to attenuate such a sliding noise. Also, Japanese Patent Public Disclosure No. HEI 8-104471 (1996) discloses a cable reel in which a sound-absorbing material 5 made of a resilient material such as a rubber or the like or a sound-absorbing material with the polytetrafluoroethylene (PTFE) resin is attached to bearing surfaces of stationary and movable member assemblies by means of clamps provided on the surfaces.
A polytetrafluoroethylene resin sheet is adhered by way of PET (polyethylene telephthalate) to a surface of a rubber sheet since the former lacks adhesion to the latter.
Although the polytetrafluoroethylene resin sheet disclosed in Japanese Utility Model Publication No. HEI 6-36040 (1994) can attenuate sliding noise on account of its high degree of lubrication, it cannot reduce noise which is caused by collision of the flat cable onto the bearing surfaces of the cable reel due to axial vibrations of the cable in a coiled manner. In particular, such unpleasant collision noise is likely to be accentuated when an engine is idling. On the other hand, the resilient sheet disclosed in Japanese Patent Publication No. HEI 8-104471 (1996) hardly attenuates sliding noise, since the lubrication between the flat cable and the resilient sheet is poor, although the sheet can reduce the collision or vibration noise.
The rubber sheet provided on its surface with a polytetrafluoroethylene resin sheet has a high lubrication due to the resin sheet, thereby reducing sliding noise and also can absorb vibration noise by means of the rubber sheet.
As shown in FIGS. 9A to 9C, however, a rubber sheet 5a, a polyethylene telephthalate (PET) film 5b and a polytetrafluoroethylene (PTFE) resin sheet 5c must be punched out into an annular shape adapted to be used, since the bearing surfaces of the cable containing chamber 3 are in an annular form. Consequently, this involves much loss of material. In particular, a total cost of the cable reel becomes high since the PTFE resin sheet is expensive.
In addition, the above sound-absorbing material 5 involves a high cost due to an increase in working steps, since the PET film is adhered to the rubber sheet through an adhesive and then the PTFE resin sheet is attached to the PET film by way of an adhesive.
Moreover, the above sound-absorbing material gives rise to a problem in that it reduces a sound-absorbing effect since the hard PET film is interposed between the rubber sheet having a sound-absorbing function and the PTFE resin sheet having a lubricative function. It is difficult to produce the PTFE resin sheet having a low thickness since it is produced by means of skiving. Consequently, the sheet on the market is usually more than 20 .mu.m. Such a thick PTFE resin sheet in addition to the hard PET film will lower the sound-absorbing function.